Superstorm Sandy forced three nuclear reactors to close by playing havoc with cooling water and electrical lines, but the nuclear industry took the pounding without suffering a major problem.

Nuclear plants are supposed to withstand hurricanes, tornadoes, earthquakes, even a direct hit from a hijacked jetliner. But an earthquake and tsunami that caused multiple meltdowns last year at a nuclear plant in Japan has raised public scrutiny on how they perform during natural disasters.

Storm-related complications were blamed this week for forcing three nuclear reactors offline – Nine Mile Point Unit 1 northwest of Syracuse, N.Y., Indian Point Unit 3 about 25 miles north of New York City and the Salem plant’s Unit 1 on the Delaware River in New Jersey.

Meanwhile, rising waters along the Barnegat Bay prompted officials to declare an “alert,” the second-lowest in a four-tiered warning system, at Oyster Creek in New Jersey. That plant had earlier been taken out of service for a scheduled refueling, meaning it was not producing power.

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Regulators and plant operators said none of the problems compromised safety.

“Hurricane Sandy once again demonstrates the robust construction of nuclear energy facilities, which are built to withstand extreme flooding and hurricane-force winds that are beyond that historically reported for each area,” said Marvin Fertel, president of the Nuclear Energy Institute, an industry lobbying group.

Some of the problems Monday were not unusual for the industry during large storms. When bad weather topples electrical lines and damages equipment, nuclear plants can be forced onto backup power to run critical systems or even shut down.

For example, Nine Mile Point’s Unit 1 reactor shut down automatically around 9 p.m. Monday when an electrical fault occurred on power lines used to send electricity from the plant to the power grid, according to the U.S. Nuclear Regulatory Commission. While that fault was probably caused by the storm, it was still under investigation Tuesday afternoon.

The second reactor at the site lost an incoming power line, which prompted a backup generator to start as a precaution. The second reactor was continuing to produce electricity. The facility serves about one million customers.

Indian Point’s Unit 3 reactor, which is about 25 miles north of New York City, shut down Monday evening because of disturbances on the electrical grid caused by the storm, regulators said. Entergy Corp., which operates the plant, said there was no risk to employees or the public. The plant was not at risk due to water levels from the Hudson River, which reached 9 feet 8 inches and were subsiding. Unit 2 continued to operate.

The churning storm kicked up debris in the Delaware River that likely caused problems for the Unit 1 reactor at the Salem plant in Hancocks Bridge, N.J.

PSEG Nuclear spokesman Joe Delmar said plant operators manually stopped the reactor early Tuesday morning when four of six recirculation pumps failed in a cooling line that turns steam heated by the reactor back into water. Plant officials suspect the storm sent large amounts of marsh mud and grass into the water, which caused problems as the debris seeped into the cooling system, Delmar said.

Because its circulation system was not functioning normally, the plant was venting built-up steam into the atmosphere, NRC spokesman Scott Burnell said. That steam is isolated from the intense radiation deep inside a nuclear reactor and does not pose a health threat, Burnell said. It is possible that very small amounts of radioactive tritium might be present in the steam.

The second Salem unit has been offline since Oct. 14 for refueling, but the nearby Hope Creek plant remains at full power. Together, the Salem and Hope Creek plants produce enough power for about 3 million homes per day.

Rising waters caused the Oyster Creek plant in New Jersey to escalate to an “alert” from the lowest emergency level, an unusual event. Officials blamed a rising tide, wind and storm surge for sending more water than normal into the plant’s water intake structure. The plant, which is shut down for maintenance, also lost its electrical power from the grid. It used backup generators to power the equipment needed to cool its reactor. Plant operator Exelon said it can generate enough electricity to power 600,000 homes.

NRC officials reported that other plants continued operating but reduced their electrical output as a precaution, including the Millstone plant’s Unit 3 reactor in Waterford, Conn., Vermont Yankee south of Brattleboro, Vt., and both reactors at the Limerick nuclear plant about 20 miles northwest of Philadelphia. The storm also appeared to knock out emergency sirens used to notify residents who live near the Oyster Creek and Peach Bottom plants in Pennsylvania, according to NRC reports.